title: Rapamycin differentially inhibits S6Ks and 4E-BP1 to mediate cell-type-specific repression of mRNA translation.
abstract: The mammalian translational initiation machinery is a tightly controlled system that is composed of eukaryotic initiation factors, and which controls the recruitment of ribosomes to mediate cap-dependent translation. Accordingly, the mTORC1 complex functionally controls this cap-dependent translation machinery through the phosphorylation of its downstream substrates 4E-BPs and S6Ks. It is generally accepted that rapamycin, a specific inhibitor of mTORC1, is a potent translational repressor. Here we report the unexpected discovery that rapamycin's ability to regulate cap-dependent translation varies significantly among cell types. We show that this effect is mechanistically caused by rapamycin's differential effect on 4E-BP1 versus S6Ks. While rapamycin potently inhibits S6K activity throughout the duration of treatment, 4E-BP1 recovers in phosphorylation within 6 h despite initial inhibition (1-3 h). This reemerged 4E-BP1 phosphorylation is rapamycin-resistant but still requires mTOR, Raptor, and mTORC1's activity. Therefore, these results explain how cap-dependent translation can be maintained in the presence of rapamycin. In addition, we have also defined the condition by which rapamycin can control cap-dependent translation in various cell types. Finally, we show that mTOR catalytic inhibitors are effective inhibitors of the rapamycin-resistant phenotype.
authors.affiliation: Department of Cell Biology, Harvard Medical School, Boston, MA 02115, USA.
authors.forename: Andrew Y
authors.initials: AY
authors.lastname: Choo
authors.forename: Sang-Oh
authors.initials: SO
authors.lastname: Yoon
authors.forename: Sang Gyun
authors.initials: SG
authors.lastname: Kim
authors.forename: Philippe P
authors.initials: PP
authors.lastname: Roux
authors.forename: John
authors.initials: J
authors.lastname: Blenis
mesh_terms: D048868:Adaptor Proteins, Signal Transducing; D000818:Animals; D002352:Carrier Proteins / Q000037:antagonists & inhibitors* / Q000378:metabolism; D018797:Cell Cycle Proteins; D039642:Eukaryotic Initiation Factors; D005786:Gene Expression Regulation / Q000187:drug effects*; D051379:Mice; D010750:Phosphoproteins / Q000037:antagonists & inhibitors* / Q000378:metabolism; D010766:Phosphorylation; D014176:Protein Biosynthesis / Q000187:drug effects* / Q000502:physiology; D019893:Ribosomal Protein S6 Kinases / Q000037:antagonists & inhibitors* / Q000378:metabolism; D020123:Sirolimus / Q000494:pharmacology*; D014157:Transcription Factors / Q000037:antagonists & inhibitors* / Q000378:metabolism
chemical_list: D048868:Adaptor Proteins, Signal Transducing; D002352:Carrier Proteins; D018797:Cell Cycle Proteins; C519509:Crtc1 protein, mouse; C499527:Eif4ebp1 protein, mouse; D039642:Eukaryotic Initiation Factors; D010750:Phosphoproteins; D014157:Transcription Factors; D019893:Ribosomal Protein S6 Kinases; D020123:Sirolimus